JPH06188470A - Bismuth layer compound-piezoelectric polymer composite - Google Patents

Abstract

PURPOSE:To make it possible to facilitate plastic work and form piezo-electric elements in various shapes by dispersing bismuth layer compound powder into a piezo-electric polymer matrix comprising a copolymer of vinylidene fluoride and ethylene trifluoride. CONSTITUTION:A piezo-electric polymer, which is a copolymer comprising vinylidene and ethylene trifluoride is used as a matrix where 5 to 90wt.% of bismuth layer compound powder is dispersed into there. It is possible to use ordinary bismuth layer powder, which can be expressed with a general formula (MxBiy) Ti4O15. Since the polymer is used as a matrix, plastic work is available so that various-shaped piezo-electric elements may by formed easily. Furthermore, since the bismuth layer compound powder 2, which is plastic, is dispersed there, it is possible to increase its Young's modulus compared with a polymer simple substance and use the powder as an element, which demands strength, such as a pressure sensor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a composite of a bismuth layer compound having piezoelectricity and a piezoelectric polymer, which can be used as a pressure sensor, a high frequency filter and the like.

[0002]

2. Description of the Related Art As ceramics having piezoelectricity,
Barium titanate (BaTiO _3), lead titanate (Pb
TiO ₃ ), lead zirconate titanate solid solution (PZT),
Bismuth layered compounds (SrBi ₄ Ti ₄ O ₁₅ ) and the like are known. For example, PZT is used as a piezoelectric actuator because it has a particularly high sensitivity. Further, the bismuth layered compound is not as high in sensitivity as PZT, but has a high strength and a high Curie temperature of 500 to 800 ° C. and can be used in a wide temperature range. Therefore, it is expected to be used as a pressure sensor.

To form a pressure sensor or the like from this bismuth layered compound, bismuth oxide (Bi ₂ O ₃ ), titanium oxide (TiO ₂ ) and strontium carbonate (SrC) are used.
O ₃ ) and other raw material powders are mixed in a predetermined ratio to prepare a powder raw material, and a molded body having a predetermined shape is formed from this powder raw material and then sintered to form a sintered body, which is then polarized to form. The method is common. Further, in JP-A-52-86198, a hot press or the like is used to apply pressure in one direction during sintering to align the crystal axes of plate-shaped crystals in one direction, thereby improving sensitivity. A method of making a bismuth layered compound is disclosed. According to this manufacturing method, the layered crystal of the bismuth layered compound is sintered in a state of being oriented in the direction perpendicular to the pressing direction, and the easy axis of polarization is aligned in the direction perpendicular to the pressing direction, so the piezoelectric sensitivity is improved. .

[0004]

As described above, since the bismuth layered compound can be used in a wide range of temperatures, it is expected to be used as a pressure sensor. However, since the bismuth layered compound itself is a ceramic, it has a hardness that is peculiar to ceramics but is fragile, and it is difficult to perform plastic working such as stretching or bending and has a small processing flexibility.

The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a novel composite piezoelectric body by compounding a bismuth layer compound to enable plastic working.

[0006]

A bismuth layered compound-piezoelectric polymer composite of the present invention for solving the above-mentioned problems is provided in a piezoelectric polymer matrix composed of a copolymer of vinylidene fluoride and trifluoroethylene, The bismuth layered compound powder is characterized by being dispersed in an amount of 5 to 90% by weight.

The bismuth layer compound has the general formula (M
A general one represented by x Biy) Ti ₄ O ₁₅ can be used. Here, M is a metal element having a valence of 1 to 5,
Various selections can be made from alkaline earth metals such as Sr, Be, Mg, Ca, Ba and Ra, alkali metals such as Li, Na, K, Rb and Cs and Pb. Further, metal elements such as Mn, Ni and Cr may coexist as long as the performance is not impaired.

The piezoelectric polymer constituting the matrix is composed of a copolymer of vinylidene fluoride and ethylene trifluoride. For example, polymers such as polyvinylidene fluoride and copolymers of vinylidene fluoride and tetrafluoroethylene are also piezoelectric polymers, but these piezoelectric polymers are difficult to polarize only by applying a voltage, and therefore roll stretching operation is performed. Etc. are required. However, since a piezoelectric polymer composed of a copolymer of vinylidene fluoride and ethylene trifluoride can be polarized only by applying a normal voltage, this piezoelectric polymer was used.

In the bismuth layered compound-piezoelectric polymer composite of the present invention, 5 to 90% by weight of bismuth layered compound powder is contained in a piezoelectric polymer composed of a copolymer of vinylidene fluoride and ethylene trifluoride as a matrix. It is dispersed. If the bismuth layered compound powder is less than 5% by weight, the Young's modulus cannot be improved. If the content exceeds 90% by weight, the shape cannot be maintained and it is difficult to form a composite.

[0010]

In the bismuth layered compound-piezoelectric polymer composite of the present invention, the piezoelectric polymer composed of a copolymer of vinylidene fluoride and ethylene trifluoride constitutes the matrix. Plastic working is possible.
On the other hand, this piezoelectric polymer alone has a Young's modulus of 0.3 × 10
^It is extremely small at ¹⁰ Pa and cannot be used for pressure sensors and other devices that require strength. However, the inclusion of the bismuth layered compound powder of ceramics in an amount of 5 to 90% by weight increases the Young's modulus by about an order of magnitude, and it can be used as a pressure sensor or the like that requires strength.

Further, in order to polarize the bismuth layered compound, a strict condition of 200 ° C. and 6 kV / mm or more was required, but a piezoelectric composed of a copolymer of vinylidene fluoride and ethylene trifluoride, which is easy to polarize. Since a polymer is used as a matrix, polarization is possible even under conditions of about 1 kV / mm at room temperature. Further, since the bismuth layered compound, the vinylidene fluoride and the trifluoroethylene copolymer have almost the same sensitivity, almost constant sensitivity can be obtained without strictly controlling the respective mixing ratios.

[0012]

EXAMPLES The present invention will be specifically described below with reference to examples. Figure 1
FIG. 3 is a cross-sectional view illustrating the structure of the bismuth layered compound-piezoelectric polymer composite of one embodiment of the present invention. This bismuth layered compound-piezoelectric polymer composite is composed of vinylidene fluoride and 3
The piezoelectric polymer 1 made of a copolymer of ethylene fluoride is used as a matrix, and the bismuth layered compound powder 2 is dispersed in the matrix.

This bismuth layered compound-piezoelectric polymer composite was formed as follows. That is, strontium carbonate (SrCO ₃ ), bismuth oxide (Bi ₂ O ₃ ), titanium oxide (TiO ₂ ), and manganese oxide (MnO) were used as starting materials, and the respective raw material powders were used with the composition ratio of SrBi ₄ Ti ₄ O ₁₅ and MnO
Was weighed so as to contain 0.1% by weight in terms of Mn weight, and wet mixed with ethanol in a pot mill for 48 hours.

The mixed powder is dried with ethanol to remove 80
It was calcined at 0 ° C. for 2 hours. The calcined powder was wet-mixed again in the pot mill for 48 hours, and dried with ethanol to obtain a powder raw material. Polyvinyl alcohol (PV
About 3% by weight of A) was added and granulated, and the mixture was fed into a mold having a cylindrical cavity with a diameter of 18 mm to obtain 1 t / cm.
Molded at a pressure of ² .

The obtained primary molded body is heated at 900 ° C. to 1050 ° C.
The mixture was heated at 0 ° C. for 2 to 10 hours for sintering, and the sintered body after cooling was pulverized to 1 to 10 μm with a grinder to obtain a bismuth layered compound powder. Next, as shown in Table 1, the bismuth layered compound powder and the powder of the copolymer of vinylidene fluoride and ethylene trifluoride were mixed in a weight ratio of 7: 3 (the temporary sintered powder was 3
0% by weight), and mix the mixed powder to a diameter of 1
100MP using a mold with a cylindrical cavity of 8mm
Molding was performed under the pressure of a to form a disk-shaped molded body. Then, this molded body was heat-treated at 150 to 200 ° C. to obtain a bismuth layered compound-piezoelectric polymer composite.

A conductive adhesive was applied to both surfaces of the obtained composite and polarized at room temperature under the condition of 1 kV / mm or more. The piezoelectric sensitivity of the obtained device was measured, and the results are shown in Table 1. Here, the piezoelectric sensitivity means the force F on the sample.
The charge per unit force (E / F, unit pC / N), where E is the amount of charge generated when the above is added. The Young's modulus of the obtained bismuth layered compound-piezoelectric polymer composite was measured, and the results are shown in Table 1.

The mixing ratio of the bismuth layered compound powder and the vinylidene fluoride / trifluoroethylene copolymer powder was changed as shown in Table 1, and the bismuth layered compound-piezoelectric polymer composite was similarly prepared. Got Similarly, the piezoelectric sensitivity and Young's modulus were measured, and the results are shown in Table 1.

[0018]

[Table 1] (Evaluation) From Table 1, it is clear that the sensitivity is constant and stable even if the mixing ratio of the bismuth layer compound and the piezoelectric polymer changes. Therefore, it is understood that the bismuth layered compound-piezoelectric polymer composite of the present invention does not require precise control of the mixing ratio and is easy to manufacture.

The Young's modulus shows a low value of 0.5 up to a mixing ratio of the bismuth layered compound powder of 4% by weight, but increases rapidly when the mixing ratio of the bismuth layered compound powder exceeds 5% by weight. It is also clear that they are doing. When the mixing ratio of the bismuth layered compound powder exceeded 90% by weight, the molded body became powdery after the heat treatment, and it was difficult to maintain the shape, and the composite body could not be formed. Therefore, in the bismuth layered compound-piezoelectric polymer composite of the present invention, the mixing ratio of the bismuth layered compound powder is 5%.
The range of up to 90% by weight is desirable.

[0020]

That is, the bismuth layered compound of the present invention
According to the piezoelectric polymer composite, since the polymer is used as a matrix, it is possible to perform plastic working, and it is possible to easily form piezoelectric elements of various shapes. Also, since the bismuth layered compound powder which is ceramics is dispersed,
The Young's modulus is higher than that of a polymer alone, and it can be used as an element requiring strength such as a pressure sensor.

Furthermore, polarization can be performed even under a much milder condition than in the case of the bismuth layered compound alone, and energy can be saved.

[Brief description of drawings]

FIG. 1 is a schematic cross-sectional view illustrating the structure of a bismuth layered compound-piezoelectric polymer composite of the present invention.

[Explanation of symbols]

1: Piezoelectric polymer (matrix) 2: Bismuth layered compound powder

Claims (1)

[Claims] 1. A bismuth layered compound-piezoelectric material, characterized in that 5 to 90% by weight of bismuth layered compound powder is dispersed in a matrix of a piezoelectric polymer composed of a copolymer of vinylidene fluoride and ethylene trifluoride. Polymer composite.